The Breda-SAFAT 12.7mm round was not as "hammer-time" as the US 50-cal round. The Italian 12.7mm had lower muzzle velocity, and less penetration against targets. The high-explosive rounds tended to explode on the surface, and the slow rate of fire (further slowed by the prop-synchronization) didn't allow rounds to follow through previous rounds' exploded holes on the surface. So the 12.7s were better than the Fulmar's 0.303-in rounds, but not by a huge amount.

The internet article notes Peter Twiss (later noted supersonic test pilot) claiming a Cr42 by out-maneuvering it through use of the Fulmar's large flaps. There is another incident (I think also from Operation Pedestal) where a trio of Cr42s shot down one of a pair of Fulmars (the leader, flown by the RN squadron commander*). I will try and find a reference online when I get another moment.

So Cr42 v Fulmar, probably a close run thing depending on who starts with the advantage. Would be a sight through - a bit like Vietnam with giant F-4 v tiny MiG-17s - but in slow motion (and without missiles).

...geoff

Later: *....not Pedestal but earlier during an Ark Royal operation. See attached link to the "Biplane Fighters" website:

I made this comment in the Hawker Henley thread:
".... at the height where it did most of it's combat, the Fulmar didn't seem that slow compared to it's opponents. However, it seemed also to be a very narrow band of height. It just couldn't go fast enough or climb fast enough to catch anything outside that band. (Need to check some more stats to see if that impression is correct!) "

Here are a comparison batch of speeds at elevation, etc for the typical aircraft the Fulmar came into combat with (except for the Bf109 and the A6M Zero). (Hopefully, I've attached them properly. ...nope, didn't work, so try the link to my flickr account)

Between 2,000 - 7,000 ft, it's not slower than most of the aircraft it would encounter - except (occasionally) the French LeO451 and their Hawk 75A-3s. It can match the Aichi Val for speed but probably not for maneuverability. The He111s were considerably slower with full bomb/torpedo loads. Unfortunately, it is not yet a simple task to gather the aircraft speeds between 2,000 - 7,000 ft for many other aircraft.

(Info comes from the William Green edited mini-books and his 'Famous Aircraft' series, and occasionally from wiki.)